Ferroelectric hafnium zirconium oxide holds great promise for a broad spectrum of complementary metal–oxide–semiconductor (CMOS) compatible and scaled microelectronic applications, including memory, low-voltage transistors, and infrared sensors, among others. An outstanding challenge hindering the implementation of this material is polarization instability during field cycling. In this study, the nanoscale phenomena contributing to both polarization fatigue and wake-up are reported. Using synchrotron X-ray diffraction, the conversion of non-polar tetragonal and polar orthorhombic phases to a non-polar monoclinic phase while field cycling devices comprising noble metal contacts is observed. This phase exchange accompanies a diminishing ferroelectric remanent polarization and provides device-scale crystallographic evidence of phase exchange leading to ferroelectric fatigue in these structures. A reduction in the full width at half-maximum of the superimposed tetragonal (101) and orthorhombic (111) diffraction reflections is observed to accompany wake-up in structures comprising tantalum nitride and tungsten electrodes. Combined with polarization and relative permittivity measurements, the observed peak narrowing and a shift in position to lower angles is attributed, in part, to a phase exchange of the non-polar tetragonal to the polar orthorhombic phase during wake-up. These results provide insight into the role of electrodes in the performance of hafnium oxide-based ferroelectrics and mechanisms driving wake-up and fatigue, and demonstrate a non-destructive means to characterize the phase changes accompanying polarization instabilities.

The presence of the top electrode on hafnium oxide‐based thin films during processing has been shown to drive an increase in the amount of metastable ferroelectric orthorhombic phase and polarization performance. This “Clamping Effect,” also referred to as the Capping or Confinement Effect, is attributed to the mechanical stress and confinement from the top electrode layer. However, other contributions to orthorhombic phase stabilization have been experimentally reported, which may also be affected by the presence of a top electrode. In this study, it is shown that the presence of the top electrode during thermal processing results in larger tensile biaxial stress magnitudes and concomitant increases in ferroelectric phase fraction and polarization response, whereas film chemistry, microstructure, and crystallization temperature are not affected. Through etching experiments and measurement of stress evolution for each processing step, it is shown that the top electrode locally inhibits out‐of‐plane expansion in the HZO during crystallization, which prevents equilibrium monoclinic phase formation and stabilizes the orthorhombic phase. This study provides a mechanistic understanding of the clamping effect and orthorhombic phase formation in ferroelectric hafnium oxide‐based thin films, which informs the future design of these materials to maximize ferroelectric phase purity and corresponding polarization behavior.

Materials with tunable thermal properties enable on-demand control of temperature and heat flow, which is an integral component in the development of solid-state refrigeration, energy scavenging, and thermal circuits. Although gap-based and liquid-based thermal switches that work on the basis of mechanical movements have been an effective approach to control the flow of heat in the devices, their complex mechanisms impose considerable costs in latency, expense, and power consumption. As a consequence, materials that have multiple solid-state phases with distinct thermal properties are appealing for thermal management due to their simplicity, fast switching, and compactness. Thus, an ideal thermal switch should operate near or above room temperature, have a simple trigger mechanism, and offer a quick and large on/off switching ratio. In this study, we experimentally demonstrate that manipulating phonon scattering rates can switch the thermal conductivity of antiferroelectric PbZrO3 bidirectionally by −10% and +25% upon applying electrical and thermal excitation, respectively. Our approach takes advantage of two separate phase transformations in PbZrO3 that alter the phonon scattering rate in different manners. In this study, we demonstrate that PbZrO3 can serve as a fast (<1 second), repeatable, simple trigger, and reliable thermal switch with a net switching ratio of nearly 38% from ~1.20 to ~1.65 W m−1 K−1.

Temperature limitations in nickel‐base superalloys have resulted in the emergence of SiC‐based ceramic matrix composites as a viable replacement for gas turbine components in aviation applications. Higher operating temperatures allow for reduced fuel consumption but present a materials design challenge related to environmental degradation. Rare‐earth disilicates (RE2Si2O7) have been identified as coatings that can function as environmental barriers and minimize hot component degradation. In this work, single‐ and multiple‐component rare‐earth disilicate powders were synthesized via a sol‐gel method with compositions selected to exist in the monoclinic C 2/m phase (β phase). Phase stability in multiple cation compositions was shown to follow a rule of mixtures and the C 2/m phase could be realized for compositions that contained up to 25% dysprosium, which typically only exists in a triclinic, P 1¯${\rm{\bar{1}}}$, phase. All compositions exhibited phase stability from room temperature to 1200°C as assessed by X‐ray diffraction. The thermal expansion tensors for each composition were determined from high‐temperature synchrotron X‐ray diffraction and accompanying Rietveld refinements. It was observed that ytterbium‐containing compositions had larger changes in the α31 shear component with increasing temperature that led to a rotation of the principal axes. Principal axes rotation of up to 47° were observed for ytterbium disilicate. The results suggest that microstructure design and crystallographic texture may be essential future avenues of investigation to ensure thermo‐mechanical robustness of rare‐earth disilicate environmental barrier coatings.

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